Python ffmpeg 子进程永远不会在 Linux 上退出，适用于 ZAEA23489CE3AAAA943406EBB28E0CD

Question

I wonder if someone can help explain what is happening?

I run 2 subprocesses, 1 for ffprobe and 1 for ffmpeg.

popen = subprocess.Popen(ffprobecmd, stderr=subprocess.PIPE, shell=True)

And

popen = subprocess.Popen(ffmpegcmd, shell=True, stdout=subprocess.PIPE)

On both Windows and Linux the ffprobe command fires, finishes and gets removed from taskmanager/htop. But only on Windows does the same happen to ffmpeg. On Linux the command remains in htop...

Can anyone explain what is going on, if it matters and how I can stop it from happening please?

EDIT: Here are the commands...

ffprobecmd = 'ffprobe' + \
' -user_agent "' + request.headers['User-Agent'] + '"' + \
' -headers "Referer: ' + request.headers['Referer'] + '"' + \
' -timeout "5000000"' + \
' -v error -select_streams v -show_entries stream=height -of default=nw=1:nk=1' + \
' -i "' + request.url + '"'

and

ffmpegcmd = 'ffmpeg' + \
' -re' + \
' -user_agent "' + r.headers['User-Agent'] + '"' + \
' -headers "Referer: ' + r.headers['Referer'] + '"' + \
' -timeout "10"' + \
' -i "' + r.url + '"' + \
' -c copy' + \
' -f mpegts' + \
' pipe:'

EDIT: Here is a example that behaves as described...

import flask
from flask import Response
import subprocess

app = flask.Flask(__name__)

@app.route('/', methods=['GET'])
def go():
    def stream(ffmpegcmd):
        popen = subprocess.Popen(ffmpegcmd, stdout=subprocess.PIPE, shell=True)
        try:
            for stdout_line in iter(popen.stdout.readline, ""):
                yield stdout_line
        except GeneratorExit:
            raise

    url = "https://bitdash-a.akamaihd.net/content/MI201109210084_1/m3u8s/f08e80da-bf1d-4e3d-8899-f0f6155f6efa.m3u8"

    ffmpegcmd = 'ffmpeg' + \
                ' -re' + \
                ' -timeout "10"' + \
                ' -i "' + url + '"' + \
                ' -c copy' + \
                ' -f mpegts' + \
                ' pipe:'
    return Response(stream(ffmpegcmd))

if __name__ == '__main__':
    app.run(host= '0.0.0.0', port=5000)

Answer 1

You have the extra sh process due to shell=True , and your copies of ffmpeg are allowed to try to attach to the original terminal's stdin because you aren't overriding that file handle. To fix both those issues, and also some security bugs, switch to shell=False , set stdin=subprocess.DEVNULL , and (to stop zombies from potentially being left behind, note the finally: block below that calls popen.poll() to see if the child exited, and popen.terminate() to tell it to exit if it hasn't):

#!/usr/bin/env python

import flask
from flask import Response
import subprocess

app = flask.Flask(__name__)

@app.route('/', methods=['GET'])
def go():
    def stream(ffmpegcmd):
        popen = subprocess.Popen(ffmpegcmd, stdin=subprocess.DEVNULL, stdout=subprocess.PIPE)
        try:
            # NOTE: consider reading fixed-sized blocks (4kb at least) at a time
            # instead of parsing binary streams into "lines".
            for stdout_line in iter(popen.stdout.readline, ""):
                yield stdout_line
        finally:
            if popen.poll() == None:
                popen.terminate()
                popen.wait() # yes, this can cause things to actually block

    url = "https://bitdash-a.akamaihd.net/content/MI201109210084_1/m3u8s/f08e80da-bf1d-4e3d-8899-f0f6155f6efa.m3u8"

    ffmpegcmd = [
        'ffmpeg',
        '-re',
        '-timeout', '10',
        '-i', url,
        '-c', 'copy',
        '-f', 'mpegts',
        'pipe:'
    ]
    return Response(stream(ffmpegcmd))

if __name__ == '__main__':
    app.run(host= '127.0.0.1', port=5000)

Mind, it's not appropriate to be parsing a binary stream as a series of lines at all. It would be much more appropriate to use blocks (and to change your response headers so the browser knows to parse the content as a video).

Answer 2

What type is the ffmpegcmd variable? Is it a string or a list/sequence?

Note that Windows and Linux/POSIX behave differently with the shell=True parameter enabled or disabled. It matters whether ffmpegcmd is a string or a list.

Direct excerpt from the documentation :

On POSIX with shell=True, the shell defaults to /bin/sh. If args is a string, the string specifies the command to execute through the shell. This means that the string must be formatted exactly as it would be when typed at the shell prompt. This includes, for example, quoting or backslash escaping filenames with spaces in them. If args is a sequence, the first item specifies the command string, and any additional items will be treated as additional arguments to the shell itself. That is to say, Popen does the equivalent of:

Popen(['/bin/sh', '-c', args[0], args[1], ...])

On Windows with shell=True, the COMSPEC environment variable specifies the default shell. The only time you need to specify shell=True on Windows is when the command you wish to execute is built into the shell (eg dir or copy). You do not need shell=True to run a batch file or console-based executable.